Sheet feeding apparatus and image forming apparatus

ABSTRACT

A sheet feeding apparatus includes a stacking portion on which a sheet is stacked, a drive source configured to generate a driving force, a pick-up member rotatable with the driving force and configured to rotate in contact with the stacked sheet to feed the sheet, a feed member configured to feed the sheet fed by the pick-up member, an elevating unit configured to raise and lower the stacking portion with the driving force to bring the sheet and the pick-up member into contact with each other, and a control unit configured to control the elevating unit, when a trailing edge of a first sheet fed to the pick-up member is upstream of the feed member and downstream of the pick-up member, to bring a second sheet stacked on the stacking portion and to be fed subsequently to the first sheet and the pick-up member into contact with each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding apparatus, and an image forming apparatus including the sheet feeding apparatus.

2. Description of the Related Art

Conventionally, an image forming apparatus, which forms an image on a sheet, has been provided with a sheet feeding apparatus that feeds stacked sheets by bringing the uppermost sheet and a feed roller separated therefrom into contact with each other every time a single feeding operation is performed. In such a configuration, in order to make an interval between the preceding sheet and the subsequent sheet (hereinafter referred to as a sheet feed interval) as small as possible during continuous printing to improve productivity, Japanese Patent No. 4249050 discusses a configuration in which the stacked uppermost sheet and the feed roller are brought into contact with each other before a trailing edge of the preceding sheet passes through the feed roller.

However, in a sheet feeding apparatus discussed in Japanese Patent No. 4249050, while an image is formed on or transferred onto sheets, the trailing edge of the preceding sheet is sandwiched between the feed roller and the stacked uppermost sheet, thereby causing a side effect of distorting the image. Further, a contact/separation operation between the uppermost sheet and the feed roller, and the timing of when driving of the feed roller is started need to be controlled independently of each other by different electronic components (a solenoid, a clutch, etc.), causing a cost increase.

SUMMARY OF THE INVENTION

The present invention is directed to a sheet feeding apparatus that is low in cost and high in productivity.

According to an aspect of the present invention, a sheet feeding apparatus includes a stacking portion on which a sheet is stacked, a drive source configured to generate a driving force, a pick-up member provided to be rotatable with the driving force of the drive source and configured to rotate in contact with the sheet stacked on the stacking portion to feed the sheet, a feed member configured to feed the sheet fed by the pick-up member, an elevating unit configured to raise and lower the stacking portion or the pick-up member with the driving force from the drive source to bring the sheet stacked on the stacking portion and the pick-up member into contact with each other, and a control unit configured to control the elevating unit. At least in a state where a predetermined number or more of sheets are stacked on the stacking portion, the control unit controls the elevating unit, at a timing of when a trailing edge in a feeding direction of a first sheet fed to the pick-up member is upstream of the feed member and downstream of the pick-up member, to bring a second sheet stacked on the stacking portion and to be fed subsequently to the first sheet and the pick-up member into contact with each other.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate an overall configuration of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 2 illustrates a sheet feeding apparatus according to the exemplary embodiment of the present invention.

FIG. 3 is a schematic perspective view of a feeding cassette.

FIGS. 4A and 4B illustrate an elevating unit that raises and lowers a stacking plate.

FIG. 5 illustrates a drive transmission path from a drive source.

FIG. 6 is a schematic perspective view of a clutch mechanism.

FIGS. 7A, 7B, and 7C respectively illustrate operations to engage and disengage the clutch mechanism.

FIG. 8 is a timing chart of a feeding operation.

FIGS. 9A, 9B, and 9C respectively illustrate continuous feeding operations when sheets are fully stacked.

FIG. 10 is a flowchart of the continuous feeding operation according to a first exemplary embodiment.

FIG. 11 is a block diagram of a control unit according to the first exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings.

FIGS. 1A and 1B illustrate a color digital printer as an example of an image forming apparatus to which a sheet feeding apparatus according to an exemplary embodiment of the present invention is applied. FIG. 1A is a perspective view of an external appearance of an image forming apparatus 100, and FIG. 1B is a schematic sectional view of the image forming apparatus 100. The image forming apparatus 100 is a full four-color laser printer using an electrophotographic process. More specifically, an image is formed on a sheet (a recording medium) S based on an image signal input to a controller unit (control unit) from an external host apparatus such as a personal computer, an image reader, or a counterpart facsimile apparatus.

An operation for an image forming unit 101 to form an image will be described below. A drum 1 of each of first to fourth cartridges PY, PM, PC, and PK is rotationally driven at a predetermined control speed in a counterclockwise direction indicated by an arrow illustrated in FIG. 1B. A belt 4 is also rotationally driven at a speed corresponding to the speed of the drum 1 in a clockwise direction (a forward direction in drum rotation) indicated by an arrow illustrated in FIG. 1B. A scanner unit 5 is also driven.

In synchronization with the above driving, a charging roller 2 in each of the cartridges uniformly charges a surface of the drum 1 to a predetermined polarity/potential at each predetermined control timing. The scanner unit 5 scans and exposes the surface of each of the drums 1 with a laser beam modulated according to an image signal for each of the colors.

Thus, an area on the surface of each of the drums 1, which has been scanned and exposed with the laser beam, becomes an electrostatic latent image corresponding to the image signal. A development unit 3 develops the electrostatic latent image formed on the surface of each of the drums 1 as a toner image. By an electrophotographic image formation process operation, as described above, a toner image is formed on the drum 1, and the toner image formed thereon is primarily transferred onto the belt 4.

A feeding cassette 9 is detachably attached to the image forming apparatus 100 on the front side thereof (on the side on which an operator operates the apparatus and on the right side of the apparatus illustrated in FIG. 1B), and is configured to allow a user to easily stack sheets and perform jam handling processing.

A pick-up roller 6 serving as a sheet feeding unit comes into contact with the sheets stacked on a stacking plate (stacking unit) 16 (see FIG. 2) in the feeding cassette 9 to feed the sheets. The sheets fed by the pick-up roller 6 are fed one by one while being separated from one another by a feed roller 7 and a separation roller 8, and are conveyed to a secondary transfer nip portion between a secondary transfer roller 12 and the belt 4 via a registration roller pair 11. The separation roller 8 is attached to a main body of the image forming apparatus 100 via a torque limiter (not illustrated), and is brought into pressure contact with the feed roller 7 by an urging unit such as a spring (not illustrated). An exemplary embodiment of the present invention is not limited to the separation roller 8. Alternatively, a separation pad may be used. In an exemplary embodiment of the present invention, any separation unit may be used as long as it can separate, when one or more sheets are fed together, the sheets from one another with a frictional force.

The sheet on which a toner image has been transferred in the secondary transfer nip portion is heated and pressurized by a fixing unit 13 so that the toner image is fixed thereto. The sheet to which the toner image has been fixed is discharged onto a sheet discharge tray 15 by a sheet discharge roller pair 14.

Next, the sheet feeding apparatus will be described below. FIG. 2 is a schematic perspective view of a sheet feeding apparatus 10. The stacking plate 16 can be raised and lowered with the sheets stacked thereon. An elevating operation of the stacking plate 16 will be described with reference to FIGS. 3, 4A, and 4B. FIG. 3 is a schematic perspective view of the feeding cassette 9, FIG. 4A is a schematic perspective view illustrating a lowered state of the stacking plate 16 in the present exemplary embodiment, and FIG. 4B is a schematic perspective view illustrating a raised state of the stacking plate 16 in the present exemplary embodiment.

As illustrated in FIG. 3, the stacking plate 16 is rotatably positioned using a stacking plate rotation support portion 36 as a rotation center. The stacking plate 16 is raised and lowered by an elevating unit (stacking unit elevating unit) 50. The elevating unit 50 urges the stacked sheets against the pick-up roller 6 by raising the stacking plate 16, and separates the stacked sheets from the pick-up roller 6 by lowering the stacking plate 16.

Even when the sheets are slightly stacked on the stacking plate 16, the elevating unit 50 raises the stacking plate 16 until the sheets are sufficiently urged against the pick-up roller 6.

The elevating unit 50 includes elevating levers 18, elevating lever rotation support portions 37, a pair of elevating cams 19, and a connecting shaft 20 for connecting the elevating cams 19 to each other.

The elevating levers 18 are provided on both sides of the feeding cassette 9, and are rotatably fixed to a casing of the image forming apparatus 100 using the elevating lever rotation support portion 37 as the rotation center. The elevating levers 18 are urged in a direction (upward direction) closer to the pick-up roller 6 by an urging member such as a spring (not illustrated). Engaging portions 17 with the elevating levers 18 are provided at both ends of the stacking plate 16. While the feeding cassette 9 is mounted and aligned on the image forming apparatus 100, the engaging portions 17 and the elevating levers 18 engage with each other, and the stacking plate 16 is raised in conjunction with rotation of the elevating levers 18. The rotation of the elevating levers 18, which are urged in the direction closer to the pick-up roller 6, is restricted by the elevating cams 19 arranged above the elevating levers 18. As illustrated in FIGS. 4A and 4B, when the connecting shaft 20 rotates upon receiving a driving force from a drive unit (to be described below), the elevating cams 19 rotate so that the elevating levers 18 rotate up and down, and the stacking plate 16 is raised and lowered via the engaging portions 17.

A drive unit 80 will be described below with reference to FIG. 5. The drive unit 80 transmits a driving force to the elevating unit 50 to raise and lower the stacking plate 16. The drive unit 80 rotates the pick-up roller 6 via a driving transmission unit.

A drive source 21 is, for example, a motor of the drive unit 80 provided in the main body of the image forming apparatus 100. A driving force generated by the drive source 21 is transmitted from a first drive gear 22 to a second drive gear 23 and from the second drive gear 23 to a chipped tooth gear 24. A solenoid (see FIG. 11) restricts the chipped tooth gear 24 and releases the restriction. Thus, the chipped tooth gear 24 selectively engages with the second drive gear 23. When the solenoid releases the restriction of the chipped tooth gear 24, the chipped tooth gear 24 engages with the second drive gear 23 so that the driving force is transmitted. Thus, the chipped tooth gear 24 starts to rotate. When the solenoid restricts the chipped tooth gear 24 at a position where the chipped tooth gear 24 rotates once and a chipped tooth portion of the chipped tooth gear 24 opposes the second drive gear 23, the driving force is not transmitted. The chipped tooth gear 24 and the elevating cams 19 are fixed to the connecting shaft 20, which is rotatably supported on the main body of the image forming apparatus 100, and rotate integrally with the connecting shaft 20. When the solenoid operates to release the restriction of the chipped tooth gear 24 based on an electric signal from a control unit (not illustrated), the chipped tooth gear 24 engages with the second drive gear 23, the driving force generated by the drive source 21 is transmitted to the connecting shaft 20 via the chipped tooth gear 24, and the connecting shaft 20, together with the elevating cams 19, rotates once.

An idler gear 31 serving as a drive transmission unit transmits a driving force to the pick-up roller 6 and the feed roller 7 via a clutch mechanism 60. Each of the pick-up roller 6 and the feed roller 7 has a tooth surface formed therein, which engages with the idler gear 31, and is rotationally driven in response to the rotation of the idler gear 31.

A clutch input gear 26 serving as a clutch input portion rotates when the driving force of the drive unit 80 is input thereto, and a clutch output gear 27 serving as a clutch output portion transmits the driving force from the drive unit 80 to the pick-up roller 6 by engaging with the clutch input gear 26. The idler gear 31 is arranged to engage with the clutch output gear 27. Thus, while the clutch input gear 26 engages with the clutch output gear 27, the rotation of the connecting shaft 20 is transmitted to the idler gear 31 so that the pick-up roller 6 and the feed roller 7 are driven. While the clutch input gear 26 does not engage with the clutch output gear 27, the rotation of the connecting shaft 20 is not transmitted to the idler gear 31.

When the connecting shaft 20 rotates once, the pick-up roller 6 and the feed roller 7 rotate. A conveyance distance of the sheet by the rotation is set to a distance that allows the sheet to be conveyed to the registration roller pair 11 on a downstream side.

Next, the clutch mechanism 60 will be described in detail below. The clutch input gear 26 in the clutch mechanism 60 engages with the clutch output gear 27 after the elevating unit 50 raises the stacking plate 16 to bring the stacked sheets into pressure contact with the pick-up roller 6. Thus, the pick-up roller 6 starts to rotate after the sheets stacked on the stacking plate 16 come into pressure contact with the pick-up roller 6. Therefore, the sheet feed interval does not vary. Even if the number of the sheets stacked on the stacking plate 16 changes and the timing of when the sheets and the pick-up roller 6 come into contact with each other deviates, the timing of when the pick-up roller 6 starts to feed the sheets is constant regardless of the amount of stacked sheets.

FIG. 6 is a schematic perspective view of the clutch mechanism 60 according to the present exemplary embodiment, FIG. 7A is a schematic view illustrating a state where the clutch mechanism 60 is disengaged, FIG. 7B is a schematic view illustrating a state where the clutch mechanism 60 is engaged, and FIG. 7C is a schematic view illustrating switching of the clutch mechanism 60 from an engaged state to a disengaged state.

As illustrated in FIG. 6, a clutch bearing 25 is fixed to the connecting shaft 20, and rotates integrally with the connecting shaft 20. The clutch bearing 25 includes keys 30. A clutch input gear 26 includes key grooves 29, a cam surface 32, and an input-side gear tooth surface 35. The clutch input gear 26 is retained in the clutch bearing 25 when the keys 30 in the clutch bearing 25 engage with the key grooves 29, and is fixed in a rotational direction of the clutch bearing 25 and is movable in a longitudinal direction (rotational axis direction) of the connecting shaft 20. The clutch output gear 27 includes a tooth surface 39 that engages with the idler gear 31 and an output-side gear tooth surface 38, and is rotatably retained in the clutch bearing 25. The clutch output gear 27 in the longitudinal direction of the cam connecting shaft 20 is fixed to the main body of the image forming apparatus 100. As illustrated in FIG. 7A, a clutch pressing spring 28 serving as an elastic member urges the clutch input gear 26 toward the clutch output gear 27.

An operation to engage and disengage the clutch mechanism 60 will be described below with reference to FIGS. 7A to 7C.

As illustrated in FIG. 7A, while the cam surface 32 provided in the clutch input gear 26 is locked by a clutch restriction rib 33 provided in the main body of the image forming apparatus 100, the input-side gear tooth surface 35 of the clutch input gear 26 separates from the output-side gear tooth surface 38 of the clutch output gear 27. With the clutch mechanism 60 thus disengaged, the driving force is not transmitted.

As illustrated in FIG. 7B, the input-side gear tooth surface 35 of the clutch input gear 26 engages with the output-side gear tooth surface 38 of the clutch output gear 27 so that the clutch mechanism 60 is engaged. With the clutch mechanism 60 thus engaged, the driving force is transmitted to the pick-up roller 6 and the feed roller 7 from the connecting shaft 20 via the idler gear 31. Thus, the engagement and the disengagement of the clutch mechanism 60 is switched by the cam surface 32, which rotates integrally with the connecting shaft 20, and the clutch restriction rib 33.

When the connecting shaft 20 rotates in the disengaged state of the clutch mechanism 60 illustrated in FIG. 7A, the clutch bearing 25 fixed to the connecting shaft 20 rotates, and the clutch input gear 26 also rotates via the key grooves 29 and the keys 30. The clutch restriction rib 33 is fixed to the main body of the image forming apparatus 100, and when the clutch input gear 26 rotates, a relative position between the clutch restriction rib 33 and the cam surface 32 is shifted.

When the clutch input gear 26 rotates by a predetermined amount, the cam surface 32 is released from the restriction by the clutch restriction rib 33. An urging force of the clutch pressing spring 28 brings the input-side gear tooth surface 35 of the clutch input gear 26 into contact with the output-side gear tooth surface 38 of the clutch output gear 27. Thus, the clutch mechanism 60 enters the engaged state illustrated in FIG. 7B.

A slope surface 40 is formed in the cam surface 32. When the clutch input gear 26 further rotates, the clutch restriction rib 33 runs onto the slope surface 40, as illustrated in FIG. 7C. The cam surface 32 is locked by the clutch restriction rib 33 again. Thus, the input-side gear tooth surface 35 and the output-side gear tooth surface 38 separate from each other.

When the connecting shaft 20 further rotates in the state illustrated in FIG. 7C, the clutch mechanism 60 enters the disengaged state illustrated in FIG. 7A. As described above, a movement mechanism 70 for moving the clutch input gear 26 including the clutch pressing spring 28, the cam surface 32, and the clutch restriction rib 33 moves the clutch input gear 26 between an engaged position where it engages with the clutch output gear 27 and a disengaged position where it disengages therefrom. More specifically, the movement mechanism 70 moves, by using the cam surface 32 and the clutch restriction rib 33, the clutch input gear 26 to a position along an axial direction of the cam connecting shaft 20 according to a rotational angle of the clutch input gear 26.

The elevating cams 19 provided in the connecting shaft 20 and the clutch input gear 26 rotate in synchronization with each other. The cam surface 32 in the movement mechanism 70 is formed so that the movement mechanism 70 moves the clutch input gear 26 to the engaged position after the stacking plate 16 is raised by the elevating cams 19 to urge the sheets stacked thereon against the pick-up roller 6.

The timing of a feeding operation of the sheet feeding apparatus 10 will be described below.

FIG. 8 is a timing chart of the feeding operation according to the present exemplary embodiment, where a rising edge and a falling edge of a line represent the start and the end of each of operations, respectively.

When a sheet feed signal is input to a control unit in response to an instruction from a user, the control unit starts to drive the drive source 21. When a predetermined timing is reached based on a count value of a timer, the above-described solenoid is sucked in based on an electric signal from the control unit so that the chipped tooth gear 24 and the second drive gear 23 engage with each other. Thus, the driving force generated by the drive source 21 is transmitted to the connecting shaft 20 via the chipped tooth gear 24, and the connecting shaft 20 starts to rotate together with the elevating cams 19 and the clutch bearing 25.

When the elevating cams 19 rotate, the elevating levers 18 rotate, and the stacking plate 16 also starts to be raised and lowered via the engaging portions 17 with the elevating levers 18. As illustrated in FIG. 8, the timing of when a sheet S and the pick-up roller 6 come into pressure contact with each other deviates depending on the amount of sheets S stacked on the stacking plate 16 (hereinafter, cases where the sheet stacking amount is large and small are referred to as “fully stacked” and “slightly stacked”, respectively).

In the present exemplary embodiment, the clutch mechanism 60 is engaged by the cam surface 32 and the clutch restriction rib 33 after the timing of when the sheet S on the stacking plate 16 and the pick-up roller 6 come into contact with each other even when the sheets S are fully stacked. Therefore, even if the sheet S and the pick-up roller 6 come into contact with each other, the feeding of the sheet S is not immediately started. As illustrated in FIG. 8, the feeding of the sheet S is not started until the clutch mechanism 60 is engaged. More specifically, the timing of when the clutch mechanism 60 is engaged is in a predetermined position during one rotation of the connecting shaft 20. Thus, the timing of when the pick-up roller 6 feeds the sheet S is constant.

Thus, even if the timing of when the sheet S and the pick-up roller 6 come into contact with each other differs, the timing of when the pick-up roller 6 feeds the sheet S is constant regardless of the amount of the stacked sheets S. After the connecting shaft 20 rotates once, the cam surface 32 and the clutch restriction rib 33 disengage the clutch mechanism 60 so that the clutch mechanism 60 enters the disengaged state, as illustrated in FIG. 7A. With the clutch mechanism 60 disengaged, the pick-up roller 6 and the feed roller 7 can be driven to rotate. Thus, the registration roller pair 11 on a downstream side does not have a conveyance resistance without back tension being applied to the sheet S. A conveyance distance of the sheet S by the pick-up roller 6 and the feed roller 7 can be freely set depending on a speed reduction ratio between the gears 27 and 31 corresponding to the one rotation of the connecting shaft 20 and a speed reduction ratio based on the diameters of the rollers. Therefore, the outer diameters of the pick-up roller 6 and the feed roller 7 do not need to be increased even if a configuration according to the present exemplary embodiment is used to eliminate a variation in the sheet feed interval.

A feeding operation performed when feeding is continuously performed will be described below with reference to FIGS. 9A to 9C. FIGS. 9A to 9C illustrate a continuous feeding operation performed when the sheets S are fully stacked on the stacking plate 16. FIG. 9A illustrates a state where the preceding sheet (first sheet) S1 is fed by the above-mentioned feeding operation, reaches the registration roller pair 11 on a downstream side, and is conveyed by the registration roller pair 11.

In the first exemplary embodiment, as illustrated in FIG. 9B, before a trailing edge of the preceding sheet S1 passes through the feed roller 7 after passing through the pick-up roller 6, the subsequent sheet (second sheet) S2 to be fed subsequently to the preceding sheet S1 and the pick-up roller 6 are brought into contact with each other. In a state illustrated in FIG. 9B where the subsequent sheet S2 and the pick-up roller 6 come in contact with each other, the clutch mechanism 60 has not yet been engaged. Thus, the feeding of the subsequent sheet S2 is not started.

As illustrated in FIG. 9C, after the trailing edge of the preceding sheet S1 conveyed by the registration roller pair 11 passes through the feed roller 7, the clutch mechanism 60 is engaged. Thus, the pick-up roller 6 feeds the subsequent sheet S2.

The above-mentioned feeding operation of the preceding sheet S1 and the subsequent sheet S2 will be described below with reference to FIG. 10. FIG. 11 is a block diagram of a control unit according to the first exemplary embodiment. As illustrated in FIG. 11, a central processing unit (CPU) 100 is connected to a drive source (motor) 21, a registration sensor 90, a solenoid 91, and a size acquisition unit 92. The CPU 100 is also connected to a read-only memory (ROM) and a random access memory (RAM) and uses the RAM as a work memory to execute a program that is stored in the ROM and corresponds to a procedure illustrated in FIG. 10. In the first exemplary embodiment, the CPU 100, the ROM, and the RAM constitute the control unit.

First, in step S101, a print job is executed from an operation unit 93 in the image forming apparatus 100 or from a computer 94 connected to the image forming apparatus 100 directly or via a network. When the print job has been executed, then in step S102, the control unit drives (turns on) the drive source 21. In step S103, the control unit sucks in (turns on) the solenoid 91 at a predetermined timing.

When the solenoid 91 is sucked in, the driving force from the drive source 21 is transmitted to the connecting shaft 20. In step S104, the control unit starts to raise the stacking plate 16. In step S105, the control unit brings the uppermost sheet S (the preceding sheet S1) stacked on the stacking plate 16 into contact with the pick-up roller 6. At this time, the clutch mechanism 60 has not been engaged. Thus, the pick-up roller 6 and the feed roller 7 have not rotated.

In step S106, when the connecting shaft 20 further rotates with the driving force from the drive source 21, the clutch mechanism 60 becomes engaged and the pick-up roller 6 and the feed roller 7 start to rotate, allowing the preceding sheet S1 to be fed. A profile of the elevating cams 19 is configured so that the stacking plate 16 starts to move down after a leading edge of the preceding sheet S1, which the pick-up roller 6 has started to feed, reaches the feed roller 7. Thus, the uppermost sheet S stacked on the stacking plate 16 and the pick-up roller 6 separate from each other.

In step S107, the registration sensor 90 detects the preceding sheet S1 that has been fed by the pick-up roller 6 and the feed roller 7. The control unit determines a timing of when the solenoid 91 for starting an operation to feed the subsequent sheet S2 is turned on based on a timing of when the registration sensor 90 has detected the preceding sheet S1 (a detection result) and on length information of the preceding sheet S1 in a conveyance direction (acquired by the size acquisition unit 92). More specifically, the control unit determines the timing of when the solenoid 91 is turned on so that a timing of when the subsequent sheet S2 and the pick-up roller 6 come into contact with each other is a timing of when the trailing edge of the preceding sheet S1 is downstream of the pick-up roller 6 and upstream of the feed roller 7. It is not desirable to bring the subsequent sheet S2 and the pick-up roller 6 into contact with each other before the trailing edge of the preceding sheet S1 passes through the pick-up roller 6. Since the feed roller 7 and the pick-up roller 6 are connected to the same gear train, the pick-up roller 6 may get driven to rotate by the feed roller 7 that is driven to convey the preceding sheet S1.

In step S108, the control unit sucks in (turns on) the solenoid 91 based on the above-mentioned timing to start the operation to feed the subsequent sheet S2. In step S109, the control unit thus starts to raise the stacking plate 16, similarly to the above. In step S110, the control unit brings the uppermost sheet S (the subsequent sheet S2) on the stacking plate 16 being raised and the pick-up roller 6 into contact with each other at the timing of when the trailing edge of the preceding sheet S1 is downstream of the pick-up roller 6 and upstream of the feed roller 7. At this time, the clutch mechanism 60 has not been engaged. Thus, the pick-up roller 6 and the feed roller 7 have not rotated.

In step S111, when the connecting shaft 20 further rotates with the driving force from the drive source 21, the clutch mechanism 60 is engaged and the pick-up roller 6 and the feed roller 7 start to rotate, allowing the subsequent sheet S2 to be fed. When the pick-up roller 6 and the feed roller 7 are to start to rotate, the trailing edge of the preceding sheet S1 has passed through the feed roller 7. The reason for this is that in the first exemplary embodiment, the separation roller 8 separates from the feed roller 7. Even in a configuration in which the separation roller 8 does not separate from the feed roller 7, to prevent the leading edges of the sheets S from being turned over or prevent the sheets S from being doubly fed, it is desirable to start rotating the pick-up roller 6 after the trailing edge of the preceding sheet S1 passes through the feed roller 7.

As described above, in the first exemplary embodiment, in a state where the trailing edge of the preceding sheet S1 is downstream of the pick-up roller 6 and upstream of the feed roller 7, the pick-up roller 6 and the subsequent sheet S2 are brought into contact with each other. Further, in the first exemplary embodiment, after the trailing edge of the preceding sheet S1 passes through the feed roller 7, the pick-up roller 6 starts to rotate. In the first exemplary embodiment, a profile of the elevating cams 19, a timing of when the clutch mechanism 60 is engaged, and an external size of the pick-up roller 6 are designed to satisfy the above two conditions.

In the above-mentioned exemplary embodiment of the present invention, the timing of when the subsequent sheet S2 and the pick-up roller 6 come into contact each other may be controlled only when the number of sheets S stacked on the stacking plate 16 is large, i.e., a predetermined number or more. Conversely, if the number of sheets S stacked on the stacking plate 16 is less than the predetermined number, the subsequent sheet S2 and the pick-up roller 6 may be brought into contact with each other at a timing of when the trailing edge of the preceding sheet S1 is downstream of the feed roller 7. More specifically, in the exemplary embodiment of the present invention, at least when the predetermined number or more of sheets S are stacked on the stacking plate 16, the subsequent sheet S2 and the pick-up roller 6 are brought into contact with each other at the timing of when the trailing edge of the preceding sheet S1 is upstream of the feed roller 7.

An interval L between the trailing edge of the preceding sheet S1 and the leading edge of the subsequent sheet S2 is made constant by the action of the clutch mechanism 60 regardless of the stacked amount of the sheets S by making the timing of starting the feeding operation of the subsequent sheet S2 relative to the preceding sheet S1 (timing of sucking in the solenoid 91 to start rotating the connecting shaft 20) constant. When the subsequent sheet S2 is conveyed to the registration roller pair 11, the clutch mechanism 60 enters the state illustrated in FIG. 9A. The foregoing operation is repeated so that the sheets S are continuously fed.

As described above, according to the first exemplary embodiment, one electronic component (the solenoid 91) can control the timing of when the pick-up roller 6 and the uppermost sheet S on the stacking plate 16 come into contact with each other and the timing of when the pick-up roller 6 starts to rotate. Further, when the trailing edge of the preceding sheet S1 is positioned between the pick-up roller 6 and the feed roller 7, the pick-up roller 6 can be brought into contact with the subsequent sheet S2. Thus, a sheet feed interval (interval L between the trailing edge of the preceding sheet S1 and the leading edge of the subsequent sheet S2) can be kept small. Therefore, a sheet feeding apparatus, which is low in cost and high in productivity, can be provided.

While the solenoid 91 controls an engagement between the chipped tooth gear 24 and the second drive gear 23 in the above-mentioned first exemplary embodiment, an electromagnetic clutch may be used to control the engagement.

While the configuration in which the clutch input gear 26 and the clutch output gear 27 engage with each other in a tooth surface shape has been described above in the first exemplary embodiment, any configuration that can transmit a driving force may be used. For example, the clutch input gear 26 and the clutch output gear 27 may come into contact with each other using a friction member having a high sliding resistance.

While the configuration in which one cam surface 32 and one clutch restriction rib 33 are provided has been described above in the first exemplary embodiment, a plurality of cam surfaces 32 and a plurality of clutch restriction ribs 33 may be provided in a rotational direction of the clutch input gear 26 so that the clutch mechanism 60 is engaged and disengaged a plurality of times with the rotation of the clutch input gear 26. Further, a plurality of cam surfaces 32 and a plurality of clutch restriction ribs 33 may be provided in a diameter direction of the clutch input gear 26 so that the clutch mechanism 60 is engaged and disengaged simultaneously by the plurality of lock portions.

While a configuration in which the pick-up roller 6 is fixed and the stacking plate 16 is raised and lowered to bring the sheet S stacked on the stacking plate 16 and the pick-up roller 6 into contact with each other has been described above in the first exemplary embodiment, the exemplary embodiment of the present invention is not limited to this. The exemplary embodiment of the present invention may have a configuration in which the stacking plate 16 is fixed and the pick-up roller 6 is raised and lowered.

Embodiments of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions recorded on a storage medium (e.g., non-transitory computer-readable storage medium) to perform the functions of one or more of the above-described embodiment(s) of the present invention, and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more of a central processing unit (CPU), micro processing unit (MPU), or other circuitry, and may include a network of separate computers or separate computer processors. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2013-198162 filed Sep. 25, 2013, which is hereby incorporated by reference herein in its entirety. 

What is claimed is:
 1. A sheet feeding apparatus comprising: a stacking portion on which a sheet is stacked; a drive source configured to generate a driving force; a pick-up member provided to be rotatable with the driving force of the drive source and configured to rotate in contact with the sheet stacked on the stacking portion to feed the sheet; a feed member configured to feed the sheet fed by the pick-up member; an elevating unit configured to raise and lower the stacking portion or the pick-up member with the driving force from the drive source to bring the sheet stacked on the stacking portion and the pick-up member into contact with each other; and a control unit configured to control the elevating unit, wherein at least in a state where a predetermined number or more of sheets are stacked on the stacking portion, the control unit controls the elevating unit, at a timing of when a trailing edge in a feeding direction of a first sheet fed to the pick-up member is upstream of the feed member and downstream of the pick-up member, to bring a second sheet stacked on the stacking portion and to be fed subsequently to the first sheet and the pick-up member into contact with each other.
 2. The sheet feeding apparatus according to claim 1, further comprising a clutch mechanism configured to transmit the driving force from the drive source to the pick-up member so that the pick-up member rotates after the sheet stacked on the stacking portion and the pick-up member come into contact with each other.
 3. The sheet feeding apparatus according to claim 2, wherein the clutch mechanism rotates the pick-up member after a trailing edge of the second sheet passes through the feed member.
 4. The sheet feeding apparatus according to claim 2, wherein the clutch mechanism includes: a clutch input portion configured to rotate when the driving force of the drive source is input thereto: a clutch output portion configured to transmit the driving force from the drive source to the pick-up member by engaging with the clutch input portion; and a movement mechanism configured to move the clutch input portion between a disengagement position where the clutch input portion disengages from the clutch output portion and an engagement position where the clutch input portion engages with the clutch output portion.
 5. The sheet feeding apparatus according to claim 1, further comprising a shaft provided to be rotatable, wherein the pick-up member feeds the sheet when the shaft rotates, wherein the elevating unit raises and lowers the stacking portion or the pick-up member when the shaft rotates, and wherein the clutch input portion rotates when the shaft rotates.
 6. The sheet feeding apparatus according to claim 5, wherein the elevating unit includes an elevating cam configured to raise and lower the stacking portion when the shaft rotates, and wherein the clutch input portion moves between the disengagement position and the engagement position while the shaft rotates once.
 7. The sheet feeding apparatus according to claim 4, wherein the movement mechanism includes: a cam provided on the clutch input portion; an elastic member configured to urge the clutch input portion toward the clutch output portion; and a clutch restriction member configured to lock the clutch input portion at the disengagement position by coming into contact with the cam urged by the elastic member, wherein, when the drive source is driven to rotate the clutch input portion, a locked state between the cam and the clutch restriction member is released so that the clutch input portion moves from the disengagement position to the engagement position, and wherein, when the clutch input portion further rotates, the cam and the clutch restriction member are locked again so that the clutch input portion moves to the disengagement position.
 8. The sheet feeding apparatus according to claim 1, wherein the elevating unit separates the sheet stacked on the stacking portion and the pick-up member from each other after the sheet stacked on the stacking portion is fed to the pick-up member.
 9. The sheet feeding apparatus according to claim 1, further comprising a separation member provided at a position opposing the feed member and configured to separate sheets with a frictional force.
 10. The sheet feeding apparatus according to claim 1, further comprising a detection unit provided downstream of the feed member and configured to detect the sheet, wherein the control unit controls the elevating unit based on a result of detection by the detection unit.
 11. The sheet feeding apparatus according to claim 1, further comprising a size acquisition unit configured to acquire information about a length in a conveyance direction of the sheet to be fed, wherein the control unit controls the elevating unit based on a result of detection by the detection unit.
 12. A sheet feeding apparatus comprising: a stacking portion on which a sheet is stacked; a pick-up member configured to come into contact with the sheet stacked on the stacking portion to feed the sheet; a feed member configured to feed the sheet fed by the pick-up member; a drive source configured to generate a driving force; an elevating unit configured to raise and lower the stacking portion or the pick-up member with the driving force from the drive source to bring the sheet stacked on the stacking portion and the pick-up member into contact with each other; and a control unit configured to control the elevating unit, wherein the control unit controls the elevating unit, at a timing of when a trailing edge in a feeding direction of a first sheet fed to the pick-up member is upstream of the feed member and downstream of the pick-up member, to bring a second sheet stacked on the stacking portion and to be fed subsequently to the first sheet and the pick-up member into contact each other.
 13. A sheet feeding apparatus comprising: a stacking portion on which a sheet is stacked; a pick-up member configured to come into contact with the sheet stacked on the stacking portion to feed the sheet; a feed member configured to feed the sheet fed by the pick-up member; a drive source configured to generate a driving force; an elevating unit configured to raise and lower the stacking portion or the pick-up member with the driving force from the drive source to bring the sheet stacked on the stacking portion and the pick-up member into contact with each other; and a control unit configured to control the elevating unit, wherein the elevating unit is configured, after a leading edge in a feeding direction of a first sheet fed by the pick-up member reaches the feed member, to separate the sheet stacked on the stacking portion and the pick-up member from each other, and wherein the control unit controls the elevating unit, at a timing of when a trailing edge in the feeding direction of the first sheet fed by the pick-up member is upstream of the feed member and downstream of the pick-up member, to bring a second sheet stacked on the stacking portion and to be fed subsequently to the first sheet and the pick-up member into contact each other.
 14. The sheet feeding apparatus according to claim 13, further comprising a clutch mechanism configured to transmit the driving force from the drive source to the pick-up member, wherein the clutch mechanism includes: a clutch input portion configured to rotate when the driving force of the drive source is input thereto; a clutch output portion configured to transmit the driving force from the drive source to the pick-up member by engaging with the clutch input portion, and a movement mechanism configured to move the clutch input portion between a disengagement position where the clutch input portion disengages from the clutch output portion and an engagement position where the clutch input portion engages with the clutch output portion. 